The effects of dietary fat on pancreatic lipase gene expression.

Abstract

Pancreatic lipase is a lipolytic enzyme involved in the hydrolysis of dietary triglycerides for absorption and utilization. Both amount and type of dietary fat have been shown to regulate pancreatic lipase; however, the mediator(s) and mechanisms for this regulation have not been identified. These studies examined the effects of dietary fat ranging in polyunsaturated to saturated ratio (PIS ratio) from 0.3 to 7.9 at low fat (11 % of energy, LF) and moderate fat (40% of energy, MF) levels, including both pre-absorptive and post-absorptive effects, on lipase content (activity), synthesis, mRNA levels and plasma ketones. Amount of fat independently increased lipase activity (p < 0.0005), synthesis (p < 0.004) and mRNA levels (p < 0.0001). Type of fat, however, affected lipase activity, but not its relative synthesis and mRNA levels. Lipase activity was significantly increased in rats fed MF diets with a high polyunsaturated fat (90% for corn oil; 172 % for safflower oil), but not significantly affected in rats fed a saturated fat (lard) or monounsaturated fat (olive oil). These results suggest that amount of fat regulates pancreatic lipase pre-translationally, whereas type of fat, specifically the degree of saturation, regulates pancreatic lipase post-translationally. Blockage of chylomicron transport out of the enterocyte with Pluronic L-81 enabled evaluation of pre-absorptive, presumably hormonally mediated, and post-absorptive, presumably peripherally mediated effects of dietary fat. Pluronic L-81 treatment decreased lipase activity 50% (p < 0.003) and mRNA levels 60% (p < 0.007) relative to control. However, Pluronic L-81 interacted with amount and type of dietary fat resulting in a blunted effect in the MF safflower group (20% lower activity and mRNA levels). These results suggest that both pre-absorptive and post-absorptive mediators play an important role in pancreatic lipase regulation by dietary fat.